In his homily for last Monday's Mass (1 Sept 2014), Pope Francis made the point that faith is something altogether different than a purely human intellectual achievement. This is a very important point, yet it is something that requires a bit more explanation.
When Christians read Mark's Gospel about the necessity of faith for salvation we take it as a given, but let's look at what Mark says again, as if for the first time:
He who believes and is baptized will be saved; but he who does not believe will be condemned (Mk 16:16)
Now why is this? What is it about faith that without it we cannot be saved; rather, we will be condemned? As with many concepts that we use regularly, e.g. love, hope, wisdom, so it is with faith that we often have a general sense about it but we really could not define it if asked. For this reason, it can be dismissed as opaque Christian jargon among non-Christians and for the same reason, it even can become meaningless for Christians who may be tempted away from faith for a variety of reasons.
The first problem in defining faith is that we use the same term for two distinct, but intertwined concepts. The tradition uses the Latin phrase fides quae creditur (the faith which one believes) to refer to the content of faith, the truth that God has revealed to us about Himself and about us through which we understand who we are, what we are made for, and the choices we are given to make. The second concept is given by the Latin phrase, fides qua creditur (the faith by which one believes). Here the term "faith" refers to an act. Yet, this act not a private act, though of course it is personal (note that private is not equivalent to personal). Rather, this act is an exchange between persons, one divine and one human. But at the same time, this act simultaneously brings together every other person who has consented to it.
In this way, we can say that this second concept, fides qua, is all about a relationship. This relationship begins with a divine act, a divine invitation brought to us through the Person of the Holy Spirit by means of his human instrument, Jesus' disciple. But a relationship requires a some level of knowledge of the other. There can be no relationship without both parties exchanging reciprocal knowledge of themselves. A relation will deepen only to the degree that this knowledge deepens.
The divine invitation is intertwined then, with the content of faith. The second movement of this act is the human response. In response to the invitation, one considers the reasonableness of the knowledge proposed and the trustworthiness of the Messenger/messenger. The development of a relationship begins only with trust and then it can move to commitment, which is an act of the will. If the invitation is reasonable and compelling then one must freely and fully choose to commit himself to the relationship; a relationship which must conform to the authentic natures of both God and man. This commitment is not so much a commitment to a proposition, but as with all acts of trust and commitment, the object of trust is always a person. In the case of Christian faith, the Object of faith is God Himself.
Human cooperation in his part of the exchange is a necessary condition for saving faith, but it is not sufficient for salvation. The exchange is not yet complete. In response to man's acceptance of this relationship, God gives to the man His very life, the fruit of which we call grace. It is in the reception of this grace which saves one. Grace is nothing more than the fruit of the relationship, it is the life of God which divinizes the recipient. In a radical communion with Life Himself, one cannot but participate in His divine life...as St. Peter says, we become partakers in the divine nature (2 Pt 1:4). This is why one is condemned for a lack of faith, one is refusing Life and Love, one is choosing his own way which is "not-God", which is "not-Love" and 'not-Life;" that is, one chooses death.
This deeper understanding of faith is important for Christians because it helps us to understand better that Jesus Christ, His Church, the Sacraments, and the entire faith is about fully and freely committing to that saving relationship of love for which we were made. Such an understanding prepares us to share more ably this truth with persons of any background. As disciples we should commit to understanding more deeply our faith so that we can more effectively live it and share it with others.